Current-limiting means



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Patented Apr. 15, 1930 UNITED STATES PATENT OFFICE FRAZER w. GAY, or NEWARK, NEW JERSEY, AssIGNon 'ro GENERAL nnnc'r'nrccou- PANY, A coaroaarrou or NEW YORK CURRENT-LIMITING MEANS Application filed March 23, 1927, Serial No. 177,816. Renewed September 16, 19 29 ing apparatus for alternating current transmission systems.

The common method of limiting the current flow in a system of the above character consists in automatically inserting either a reslstance or-a reactance 1n the -transmission line upon the occurrence of a short circuit or other cause producing a sudden surge of current in the line. The devices used for insert-' ing such resistances or reactances are relatively slow acting and an excessive and dangerous current may be permitted to pass through the line, resulting in possible injury to the transmission system and to the generating apparatus, before such devices operate to limit the current flow. Furthermore the switching of large currents by means of such devices is extremely difiicult and results in their rapid depreciation and in ineflicient operation. p a In the transmission systems where a resistance or a reactance is permanently included in the line for preventing'excessive current flow the voltage drop and resulting power loss due to the presence of such current limiting means makes the'costs of such an installation prohibitive. This power loss furthermore, increases in pro ortion to an increase in the protection a orded.

An object of the present invention is to provide current limiting apparatus adapted to avoid the disadvantages and objections above pointed out and which operates upon a current rise to immediately check such current rise and reduce the same to .a relatively low value before the main line circuit breaker operates the arrangement and character of the apparatus being such that when it is applied to a circuit it produces but a negligible potential drop therein during normal opera- A feature of the invention is to provide apparatus ofthe above character that is of simple construction and easily installed and which is reliable in operation.

Other features and advantages will become apparent from the specification,

in connection with the accompanying drawings wherein the invention is embodied in concrete form.

In the drawings:

Figure 1 is a wiring diagram illustrating the current limiting apparatus applied to a three phase alternatin current transmission line, the current limiting apparatus having an inductive reactance normally included in each phase, and

Figure 2 1s a Wiring diagram similar to Figure 1, but illustrates the current limit- 7 ing apparatus as having an inductive reactance and a condenslve reactance' normally included in each phase.

. Referring to Figure 1, a, b, and 0 represent the three conductors of a three phase alternating current transmisison line. Coupled in series with each conductor a, b and-c is a variable inductivereactance A of relative low impedance. A condensive reactance B connected in series with a low resistance 1' and a spark gap C, comprise a circuit that is connected in parallel with each inductive reactance A. The inductive reactance'A is adjusted so that its impedance at the frequency of'the system is equal in magnitude to the impedance of the condensive reactance B.

Contacts p of a switch Y are included in a cir-' cuit that is connected in parallel with the resistance r and spark C in each phase. The terminal spheres c and 0 of the spark gaps C are adjustably spaced apart. A current transformer F is provided in each conductor a, b and 0. Each current transformer F isadapted to energize the operating coil of a normally open relay H. The .contacts of re-- lays H are connected in parallel in a control circuit M. The control circuit M is connected to a supply source by means of a manually operated knife switch I. Theoperating coil E of the switch Y is connected in the control circuit M so as to be in series with the contacts of relays H. A normally open auxiliary switch K is included in the control circuit M and is arranged to be operated by the switchY. The operating coil N of a main line circuit breaker Z is included in series taken with the contacts of auxiliary switch K in the control circuit M.

The operation of the current limiting device is as follows Should an excessive current pass over the transmission line due to a short circuit or other cause, the spark gaps C immediately break down and current passes through the condensive reactances B in parallel with the inductive reactances A, though this current is somewhat limited owing to the presence of the spark gaps and the resistance 1". The impedance of the transmission line increases upon the establishment of these parallel circuits, thereby causing the flow of current in the line to beimmediately checkedto some extent.

.As the excessive current passes through the transmission line the transformers F are energized to the extent of causing the energization of the operating coils of the relays H. These relays operate to bridge their contacts, thereby closing the control circuit M-extending through the operating coil E of the switch Y. Switch Y closes, causing the spark gaps C and resistances r to be by-passed, thereby establishing a closed circuit between each of the inductive reactances A and its cooperating condensive reactance B.

Inasmuch as the impedance of each of th inductive reactances A at the frequency of the system is equal in magnitude to the impedance of each of the condensive reactances B, and asthe current in the inductive reactances A lags ninety degrees behind the impressed E. M. F whereas the current in the condensive react-ances B leads the impressed E. M. F. by ninety degrees, a resonant circuit is established in each of the three sets of parallel circuits consisting of an inductive reactance A and a condensive reactance B. The E. M. F. impressed upon these parallel circuits may therefore rise to a high value but the current passing through the transmission line is reduced to a very low quantity.

I As the switch Y closes it causes the closing of the auxiliary switch K: The closing of auxiliary switch K establishes a circuit for the operating coil N of the circuit breaker Z. The circuit breaker Z thereupon operates to open the transmission line at a time when the current passing through this line has been. reduced to a very low value. Consequently no arcing takes place at the contacts of this circuit breaker during its opening operation. After the opening of the circuit breaker Z the switches H drop out causing the opening of the switch Y. Upon reclosing the circuit breaker Z the current limiting apparatus is ready for another operation.

If desired, the current transformer F may be included in the spark gap circuits instead of in the circuits of the inductive reactances as illustrated.

The inductive reactances A may take the form of inductance coils of reactors and the condensive reactances B may be condensers or other devlces having capacitance.

In the arrangement illustrated in Figure 2, each inductive reactance A and its associated condensive reactance B are normally connected'inseries. Inasmuch as the impeddegrees, whereas the E. M. F. consumed in the inductive reactance leads the current by an equal amount, the potential drop across these reactances is very small and is due to the resistance of these members.

Power transmission circuits having a series capacitance introduced therein to neutralize or compensate the inductive reactance of the circuit between the dynamo-electric machines of the system for improving the voltage regulation and for increasing the power limit of the transmission system are described and claimed in the applications of Clifford A. Nickle, Serial No 24,243, filed April 18, 1925, for electrical power transmission and Harry R. Summerhnyes, Serial No. 165,236 filed February 1, 1927, for systems of distribution both of which are assigned to the same assignee as the present application.

Each of the spark gaps C and its associ ated resistance 1' is in a circuit that is parallel with a condensive reactance B and one pair of contacts 0 of a double throw switch X. During normal operation the operating rod of switch X is positioned so that contacts 0 of this switch are bridged. The second air of contacts p of the double throw switcii X are in a circuit that is parallel with the inductivereactance A and the condensive reactance B. The circuit for the operating coil L of the double throw switch X extends through the contacts of an auxiliary switch K. s As in the arrangement illustrated in Figure 1, the auxiliary switch K is operated by a switch Y that is arranged to by-pass the spark gaps C and resistances r. The operating 0011 E for switch Y is in the control circuit M. Control circuit M is connected by the knife switch I to a so urce of supply. .The contacts of relays H arearranged In parallel in the control circuit M and are in series with the operating coil E. Current transformers F are included in the spark gap circuits and are arranged to energize the operating coils of the relays H. The main line circuit breaker Z has its operating coil N in the control circuit M. The operating coil N of the circuit breaker'Z is arranged to be energized upon the closing of an auxiliary switch S. Auxiliary switch S is operatively connected to the operating rod of double throw switch X. During normal operation auxiliary switch S is open and the operating coil N of circuit breaker Z is deenergized.

In operation, the line current flows through contacts 0 of switch'X and through the in ductive reactances A and condensive reactances B in series. Should an excessive current pass over the transmission line the spark gaps C break down immediately and a portion of the line current passes through the spark gap circuits and through the inductive reaetances A, where the entire impedance value" of these reactances act to limit this excessive current. The transformers F are energized to cause the energization of the operating coils of the relays H. These relays operate to hrid e their contacts, thereby c'los ing the circuit extending through the opY- erating coil E of the switch.Y. Switch closes, causing the spark gaps C and resistances r to be by-passed. Auxiliary switch K closes along with switch Y and causes the energization of the operatin coil L of the double throw switch X. he double throw switch X operates to bridge contacts p, thereby causing each of the inductive reactances A to be placed in'a circuit that is parallel with that of its cooperating condenslve reactance B. The current in each of the line conductors a, b and a now passes through the bypass including the contacts D of switch Y and in parallel through the inductive reactances A and condensive reactances B. The high impedance of this resonant circuit causes the current in the main line to be reduced to a very low quantitiy.

The auxiliary switch S closes upon the operation of the double throw switch X and establishes a circuit for the operating coil N of the main circuit breaker Z. The main circuit breaker Z thereupon operates to open the transmission line.

After the opening "f the circuit breaker Z the switches H- drop out causing the 0 ening of switch Y. U on the reclosing o the double throw switch and the circuit breaker Z the current limiting means is ready for another operation.

It is to be noted that before the circuit breaker Z opens, the current in the conductors a, b and 0 has been reduced below normal full load value.

The spark gaps ma other type of rapi valvesor the may be replaced b any y operating e ectric be omitted entirely, in

w ich. event t e resistances r-would be omitte also. Instead of omittin the s ark gaps,

- the switch Y may be omitte inw ich event the resonant circuits will continue across the spark gaps untilthe main circuit breaker operates to open'the line.

As many changes could be made in the above construction and many a parently widely different embodiments of t is invention could be made without departin from the scope thereof, it is intended that a lmatter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination with an electric circuit, an inductive reactance and a condensive reactance, and means operative in accordance with the current in said circuit for placing said inductive reactance and said condensive reactance in parallel relation in said circuit upon the occurrence of current above a predetermined value therein.

2. In combination with a transmission line,

current limiting apparatus including an in-. ductive reactance and a condensive reactance, said inductive reactance and said condensive reactance having equal reactances at the frequenc of the system, and means operative in accor ance with the current in-said transm1ss10n line for placing said lnductlve reactance and said condensive reactance in paral-Z 7 with said inductance coil upon the occurrence of an excessive current flow in the line to thereby limit the current in the line. I

4. In combination with a transmission line, an inductance coil arranged in seriesin said line, a condenser, and a rapidly. operatin valve associated with said condenser, said valve acting to cause said condenserto be placed in multi le relation with said inductance coil 'shoul the current inthe transmis sion line exceed a predetermined value, thereby reducmg the flow of current in theline.

5. Current limiting apparatus for a trans- I mission circuit comprlsmg, an inductance 'coil arranged in senes in the transmission circuit, a condenser, a spark ap associated with said condenser, a switch or by-passing said s ark ap, and means responsive to cum. rent ow or controlling said switch, said current responsive means acting upon a sudden current rise vin the transmission circuit to cause the closing of said switch'to by-fass said spark gap and effect the placing o the condenser in parallel with the inductance coil in the transmission circuit.

6. In a transmission circuit, aninductive reactance and a condensive reactance arranged in series ,in the circuit to provide a normal substantially neutralized impedance, and means excited by sudden current rise in the circuit operating to 'place these .reactances in parallel relation in the circuit to thereby establish a resonant circuit and'reduce the.

' I I I I O O 7. In a transmission clrcuit, an inductance coil and a condenser connected in series in the transmission circuit whereby the capacity of the latter normally compensates the impedance of the former, a spark. gap in shunt across the condenser adapted to by-pas's current around said condenser when the current in the transmission circuit rises to a predetermined' value, a switch in shunt across said spark gap, means responsive to current flow in the spark gap circuit for causing said switch to close to by-pass current around said spark ap, and a second switch, controlled by said rst named switch, for opening the circuitof the shunted condenser and thereafter connecting said condenser in multiple relation with said inductance coil, thereby establishing a high impedance in the transmission line and reducing the current flow therein to a safe value. 8. In a transmission circuit, an inductance coil and a condenser connected in series in the transmission circuit whereby the capacity of the latter normally compensates the impedance of the former, a spark ga in shunt across the condenser adapted to y-pass current around said condenser when the current in the transmission circuit rises to a predetermined valve, a switch in shunt across said spark gap, means responsive to current flow in the spark gap circuit for causing said switch to close to by-pass current around said spark-gap, a second switch actuated by the .c osing of said first named switch to open the condenser circuit and thereafter connect said condenser in multi le relation with said inductance coil to there y reduce the current flow in the transmission line, and a circuit breaker controlled by said second switch and arranged to open the transmission circuit after the current flow in the transmission line has been reduced to a low value.

- said circuit breaker after the current flow in said circuit has been reduced.

11. In combination, an alternating current circuit, a circuit breaker therein, an inductive reactance and a condensive reactance associated with said circuit, switching means operative in accordance with the current in said circuit for placing said inductive reactance and condensive reactance in parallel relation in said circuit when the current in said circuit exceeds a predetermined value, and means interlocked with said switching means for openingsaid circuit breaker after said reactances have been connected in parallel relation in said circuit.

12. In combination, an alternating current circuit, a circuit breaker therein, means for openin said circuit breaker, an inductance coil and a condenser connected in series relation in said circuit and normally arranged for series resonance at the normal frequency of said circuit, switching means operative upon the occurrence of current above a predetel-mined value in said circuit for reconnecting said inductance coil and said condenser in parallel relation to establish a parallel resonant circuit in series relation with said cir cuit, and auxiliary switching means controlled by said switching means for controlling the opening means of said circuit breaker after the reconnection of said inductance coil and condenser in said circuit.

In testimony, that I claim the invention set forth above I have hereunto set my hand this 21st day of March, 1927.

FRAZER W. GAY.

9. Current limiting apparatus for a transstantially neutralized impedance, and an electrio valve in shunt across the condenser adapted to automatically by-pass current around said condenser when the current in the transmission circuit rises to a predetermined value and effect the establishment of parallel circuits for the inductance coil and the condenser, thereby producin current resonance and reducing the current tiew in the transmission line to a safe value.

10. In combination, an electric circuit, a circuit breaker therein, inductive and condensive reactance devices associated with said circuit, switching means operative in accordance with current above a predetermined value in said circuit for connecting said inductive and condensive reactance in said circuit to reduce substantially the current therein, and means associated with said switchin means and arrangedfor effecting opening 0 

